The present invention relates generally to gas turbine engines, and, more specifically, to compressor stators therein.
In a gas turbine engine, air is pressurized in a compressor and mixed with fuel in a combustor and ignited for generating hot combustion gases which flow through one or more turbine stages which extract energy therefrom. A high pressure turbine is joined to a compressor rotor for powering the compressor, and a low pressure turbine is typically provided for powering a fan disposed upstream of the compressor in a typical turbofan gas turbine engine configuration.
In a typical multistage axial compressor, many rows of rotor blades extend radially outward from the compressor rotor for pressurizing in turn the air channeled therethrough for increasing the pressure thereof. The compressor rotor is mounted inside a compressor stator from which extends radially inwardly a plurality of rows of stator vanes.
The stator vanes are either variable or fixed in angular pitch relative to the axial, downstream direction of the air being pressurized. A variable vane has a spindle which extends through the compressor casing and is suitably actuated for adjusting the angular rotation or pitch thereof. The fixed stator vanes are mounted to the casing individually or in multiple vane sectors for each row.
A typical vane sector includes several stator vanes extending radially inwardly from an outer band, and fixedly joined thereto. The outer band is arcuate and includes forward and aft rails which are mounted in a circumferentially extending slot in the compressor casing having corresponding forward and aft mounting hooks therefor. The vanes are thusly suspended radially inwardly from the surrounding compressor casing, with the inner ends thereof being disposed radially above the compressor rotor between blade rows.
The sectors may also include inner bands fixedly joined to the vane inner ends. An arcuate seal may be mounted to the inner bands for sealing the stationary vane sectors from the rotating compressor rotor during operation.
As the air is pressurized during operation, aerodynamic reaction force is carried through the vanes and into their outer bands. The outer bands must therefore be circumferentially retained in the casing to withstand the aerodynamic reaction forces.
A typical compressor casing is split in two semicircular half casings which are fixedly joined together in a complete ring at corresponding horizontal flanges at diametrically opposite ends of the half casings. The vane sectors are installed individually into each half casing by being circumferentially inserted into the corresponding retention slots thereof until each half casing receives its complement of sectors, typically ranging from about four to six.
The aerodynamic reaction forces are restrained by providing a stop or key at one of the horizontal flanges in each half casing against which the outer band of an adjacent vane sector may circumferentially abut for preventing further circumferential movement. The additional vane sectors in each half casing circumferentially abut each other at their outer bands. In this configuration, the reaction forces in each of the vane sectors is carried through their corresponding outer bands into the next adjoining outer band until the reaction forces are collectively carried through the single key in each half casing.
Accordingly, the first vane sector in each half casing directly abuts the sector stop and must not only carry the aerodynamic reaction forces generated in its vanes, but also the aerodynamic reaction forces generated in each of the circumferentially adjoining vane sectors of the half casing. The last vane sector in each half casing therefore carries only its portion of the reaction forces to its neighbor.
Since the compressor is a rotary component it is subject to vibration in addition to the aerodynamic reaction forces. The sectors are therefore subject to vibration and wear from the vibratory and aerodynamic reaction forces. Since each vane sector is circumferentially loaded in turn by its neighbor in each half casing, the sector closest to the stop is most highly loaded, with the circumferential reaction loads in its neighbors decreasing in turn to the last sector in the half casing which experiences the least circumferential reaction load.
But for the loading experienced by the vane sectors, they are substantially identical in configuration and operation. However, the increased circumferential loading from sector to sector causes correspondingly different rates of wear between the outer bands and the stator casing and different levels of vibratory response in the vanes. The high loaded vane sectors are therefore subject to more wear and vibration than the low loaded vane sectors which correspondingly decreases the useful life of the sectors and the casing in which they are mounted.
Accordingly, it is desired to provide an improved compressor stator for accommodating the aerodynamic reaction forces carried between the vane sectors and the casing.